This research sets out to develop sampling instrumentation by which to assess the occupational exposures of people to aerosol fractions most relevant to ill-health. Such instrumentation is essential for future epidemiology, risk estimation and the setting of occupational exposure limits (OELs) for a whole range of aerosol-related disease, including asthma and chronic pulmonary obstructive disease. It is timely in the light of the new standards for aerosol exposures which are emerging in the United States and worldwide. The particular instrumentation, which is the subject of the proposed research, is unique in that it will enable aerosol sampling of the relevant fractions to be carried out at much lower sampling flowrates than is currently the practice. This means in turn that much smaller and lighter sampling pumps (already available commercially) can be used, with associated much improved convenience to all workers, but especially those who have difficulty with existing systems (e.g., older workers, some females and - in the wider context of environmental exposure assessment - children). The research has two scientific components. Firstly, it will use current new knowledge about the physical sampling characteristics of aerosol samplers to develop scaling laws so that new samplers for given health-related fractions, specifically inhalable and thoracic (as defined by the ACGIH), can be designed to operate at much lower flowrates than existing devices. Secondly, the resulting new devices will be tested and calibrated in the laboratory (and modified as appropriate) and then validated against current reference instruments in the field at nickel industry primary production facilities. The latter will enable examination of the feasibility of measuring metal aerosol exposures from the much smaller amounts of material that will be collected using the new devices. The initial development work will be carried out in the purpose-built wind tunnel, and the analytical assays for the samples obtained in the workplace studies will be performed by ICP-MS in the Class 100 clean facility, both at the University of Michigan.